What is Lighthouse?

Lighthouse is an ARC managed HPC cluster available via a subscription to researchers who provide their own hardware. Lighthouse provides the same functionality as the Flux Operating Environment (FOE). All computational work is scheduled via the Slurm resource manager and task scheduler. To decide what hardware is best for your research and request an allocation, please contact arcts-support@umich.edu.

Who can use Lighthouse?

Lighthouse is available for:

  • Researchers who receive funds from external funding agencies for purchasing equipment.
  • Researchers who have workflow and/or infrastructure needs that differ significantly from those that can be met by other ARC services (i.e., Great Lakes or Armis2).

Lighthouse is not suitable for HIPAA or other sensitive data.

What forms do I need to fill out?

  1. The Principal Investigator (PI) should email arcts-support@umich.edu to decide on hardware needs.
  2. The PI needs to request a Slurm account from arcts-support@umich.edu, specifying users that can access the account and payment details.
  3. Each user given access to the account must request a user login. Please refer to the Lighthouse User Guide for additional steps and usage information.

How much does Lighthouse cost?

Lighthouse owners have two types of charges:

  1. One-time purchase of compute hardware, which must be supportable by ARC.
  2. A monthly charge per node, regardless of type, which accounts for data center, rack, power, networking, and staff costs. There are two rates, one which includes costs for commercial software and another which only includes software without a charge (e.g., open-source software), Matlab, and the Intel compilers. For current prices, see the HPC rates page.

What should I do if I receive a Bad Request error when accessing Open OnDemand?

If you receive a “Bad Request: Your browser sent a request that this server could not understand. Size of request header field exceeds server limit.” error, please clear your browser’s cookies and try to access Lighthouse OnDemand again.

This error can occur when the request header sent by the browser becomes too large. This is typically caused by accumulated cookies and cached data for a specific site; in some cases, corrupted cookies can also contribute to the problem.

The vendor of Open OnDemand stated that, currently, it does not do cookie/cache clean-up. We recommend using your browser in incognito mode to avoid this potential issue.

What is the difference between GiB vs GB, MiB vs MB?

A gibibyte (GiB) and a gigabyte (GB) are sometimes used as synonyms, though technically they do not describe the same amount of data capacity. What’s the difference? A gibibyte is a unit of measurement for data capacity in computing, and is based on powers of two. A gigabyte is also a unit of measurement for data, but is based in powers of 10. For example, 1 GiB equals 1,024 MiBs and 1 GB equals 1000 MiBs. This concept can be applied to the other prefixes. With the expansion of data capacity, gigabytes have become a more outdated unit of measure when compared to gibibytes. To be as accurate and consistent as possible, Slurm, slurm mail, and our additional tooling uses binary byte notation (GiB, MiB, etc) to measure data capacity.

Can I use SSH key-based authentication to access Lighthouse?

Unfortunately, this is not currently possible. We use Kerberos, a network authentication protocol which utilizes a different system based on tickets and symmetric-key cryptography. This system isn’t compatible with the public-private key pair used in SSH key-based authentication.

While we understand the convenience of SSH keys, it’s crucial that we prioritize our system’s security, which Kerberos affords us through centralized and time-sensitive ticketing control.

How do I view the usage on my account?

To view TRES (Trackable RESource) utilization by user or account, use the following commands (substitute your values for bolded parts):

Shows TRES usage by all users on account during date range:

sreport cluster UserUtilizationByAccount start=mm/dd/yy end=mm/dd/yy account=test --tres type

Shows TRES usage by specified user(s) on account during date range:

sreport cluster UserUtilizationByAccount start=mm/dd/yy end=mm/dd/yy users=un1,un2 account=test --tres type

Lists users alphabetically along with TRES usage and total during date range:

sreport cluster AccountUtilizationByUser start=mm/dd/yy end=mm/dd/yy tree account=test --tres type

Possible TRES types:


For more reporting options, see the Slurm sreport documentation.

What are the SSH pub keys for Lighthouse?

If you wish to pre-populate your SSH client configuration with the publicly available keys for Lighthouse, they are as follows:


lighthouse.arc-ts.umich.edu,lh-login?.arc-ts.umich.edu,lh-campus-login?.arc-ts.umich.edu,,, ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBHWel/rAXqIJYxexVzMSlgy/fICWukn8DaOGMPpAomH1E5AhCjrH2zMMTJHtXYsRA+brm/sTbn21Zw+pgpgJSYA=


lighthouse.arc-ts.umich.edu,lh-login?.arc-ts.umich.edu,lh-campus-login?.arc-ts.umich.edu,,, ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAICwaAq9LI48vVO4qbt35Xfz1pi+RE1Krq1iIeJQqoFEw


lighthouse.arc-ts.umich.edu,lh-login?.arc-ts.umich.edu,lh-campus-login?.arc-ts.umich.edu,,, ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAIEA16eDiBWF3SgPQXEeJsH8dsxO8x3o5KkdqWMg/lK57Kpwf4QGXJNvYy0jxSAuKTRim/ob6+nDRH8zIOwnl9tlyEw+8VN3WR8nqBqxX6Km2yzTOMO8Lh7fLuMTZHOdEz0uOn6tBP8LTMtHN9h/fANjKFVl8N+jsejMXrPf0w7jGjc=

On a Mac or Linux machine you’ll add the keys to your known_hosts file.

On a Mac this file is: /Users/<username>/.ssh/known_hosts

On Linux: /home/<username>/.ssh/known_hosts

The known_hosts file should have 644 (i.e. -rw-r--r--) permissions.

If you are using an SSH client that is not part of your operating system (e.g. Windows using PuTTY), please see the client documentation referring to host key verification.

A good start for PuTTY users can be found in the Putty FAQ (section A.2.9 “Is there an option to turn off the annoying host key prompts?)”

If you have questions, please send email to arcts-support@umich.edu.

Order Service

Principal Investigators: Email arcts-support@umich.edu before including hardware in a proposal or purchasing hardware.  Once a plan is in place, you will work with support to get a subscription to Lighthouse for each node.

You also need a Lighthouse user login to access your nodes.

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